Ytterbium-doped tantalum pentoxide waveguides: spectroscopy for compact waveguide lasers

Ytterbium-doped materials are common gain media in high-performance laser systems. In this work, the first spectroscopic investigation of ytterbium-doped tantalum pentoxide (Yb:Ta2O5) for compact waveguide laser applications is presented

Sub-wavelength focusing of high intensities in microfibre tips

Sub-wavelength efficient intensity confinement has been demonstrated in nanostructured optical microfibre tips. Focus Ion Beam (FIB) milling was used to nanostructure gold-coated optical microfibre tips and form apertures at the apex. Simulations were carried out to optimize the device design. Enhanced transmission efficiency (higher than 10-2) was achieved in spot sizes of ~λ/10. Nanostructured microfibre tips have the potential for a number of applications including optical recording, photolithography and scanning near-field optical microscopy (SNOM)

Spectroscopy of ytterbium-doped tantalum pentoxide rib waveguides on silicon

The design, fabrication and spectroscopic characterization of ytterbium-doped Ta2O5 rib waveguide are described. The waveguides are fabricated on silicon substrates and operate in a single mode at wavelengths above 970 nm. The peak absorption cross-section was measured to be 2.75 x ~10-20 cm2 at 975 nm. The emission spectrum was found to have a broad fluorescence spanning from 990 nm to 1090 nm with the fluorescence emission peak occurring at a wavelength of 976 nm. The excited-state life time was measured to be approximately 260 µs

Ytterbium-doped tantalum pentoxide waveguide lasers

We have demonstrated a Yb:Ta2O5 waveguide laser fabricated by RF magnetron sputtering on oxidised silicon. The waveguide laser was end-pumped with a laser diode at 977 nm and lasing was observed between 1015 and 1020 nm. The launched pump power threshold and slope efficiency were measured to be ~25 mW and 1.78 %, respectively

In vacuo measurement of the sensitivity limit of planar Bragg sensors

We present the direct measurement and modeling of the sensitivity limit of an integrated refractive index sensor for the detection of molecular monolayers. Direct UV writing can be used to fabricate a wide range of integrated optical devices particularly Bragg gratings. These Bragg gratings are inherently sensitive to temperature and strain

Waveguide lasers in ytterbium-doped tantalum pentoxide on silicon

A waveguide laser in an ytterbium-doped tantalum pentoxide film is reported. The waveguide is formed of a rib of sputtered tantalum pentoxide on top of oxidized silicon with an over-cladding of silica. Emission at a wavelength of 1025nm was achieved with an absorbed pump power threshold and slope efficiency of ≈ 29mW and 27%, respectively, for a cavity formed by a high reflector mirror and an estimated 12% Fresnel reflection from the bare end-face at the output

CMOS-compatible high index contrast ytterbium-doped tantalum pentoxide rib waveguide lasers

Waveguide based solid-state lasers are key components in the quest to realise a compact, robust fully integrated optical circuit with advanced functionality including pulsed operation. Ta2O5 has been a promising host material for the realization of an integrated rare-earth doped waveguide laser as it offers many important attributes such as good ability to host rare-earth ions, a high refractive index (n ~ 2.124 at λ ~ 980 nm) and a large third order nonlinearity. Here, we present an integrated rib waveguide laser in Yb:Ta2O5 with quantification of the laser slope efficiency and threshold in respect to absorbed pump power as well as presenting its lasing spectrum. Symmetrical rib waveguides with a thickness of 1 µm defined by a shallow etch of 150 nm were fabricated in Yb:Ta2O5 and encapsulated in silica cladding. These waveguides were designed for single mode operation for wavelengths ranging from 970 nm to 1100 nm, covering typical operational regions of Yb-doped materials. The fabrication process used conventional CMOS technologies which have been previously reported, where spectroscopic characterisation of similar Yb-doped waveguides was included

Thulium-doped tellurite fiber for s-band amplification

Spectroscopy measurements and the first demonstration of fiber gain in thulium doped tellurite for S-band amplification is reported. The gain extends to longer wavelength than in fluorides showing improved overlap with the C-band EDFA

Spectroscopy of Tm³⁺-doped tellurite glasses for 1470 nm fibre amplifier

Three thulium doped tellurite glass compositions have been investigated. The 1470 nm transition is radiative in these tellurite glasses and the radiative lifetimes are in the range of 350 to 470 µs. The 1470 nm fluorescence is broad with a full width at half maximum of 105 nm. Fibers have been drawn from these glasses with a loss of 0.7 dB/m at 1300 nm. A fiber with an OH fundamental absorption of 200 dB/m at 2.99 µm has an OH first overtone absorption of 0.3 dB/m at 1480 nm. The overlap between the thulium ion 1470 nm emission and the hydroxyl absorption depends on glass composition. Tellurite glasses can accept large concentrations of Tm3+ ions and, as long as the hydroxyl level can be kept low, the effect of concentration quenching can be minimized. Tm3+-doped tellurite glasses represent a viable alternative for the next generation of active components for S-band optical amplifiers. It can be pumped at 795 nm with an absorption of ~38 dB/km/ppm and codoped with Ho3+ to avoid self-termination of the 1470 nm transition. It can also be pumped at 1212 nm as efficiently as at 795 nm, but diodes are not yet available at this wavelength. Using available pump wavelengths of 1064 nm and 1047 nm will require fiber lengths 15 times longer than pumping at 1212 nm

Mid infrared GeTe₄ waveguides on silicon with a ZnSe isolation layer

GeTe4 waveguides were designed and fabricated on silicon substrates with ZnSe isolation layer. GeTe4 has a refractive index of 3.3 and it needs a lower refractive index isolation layer to realise waveguides on silicon. Numerical modelling was carried out to calculate the thickness of the isolation layer (ZnSe, refractive index ~2.4) required to achieve low loss waveguides. For a loss between 0.1 and 0.01dB/cm it was found that ~ 3 µm thick ZnSe film is required at 6.5 µm wavelength. ZnSe thin films were deposited on silicon, GeTe4 waveguides were fabricated by lift-off technique and were characterised for mid-infrared waveguiding. <br/